Irrigation requirements for Eriogonum seed production

Irrigation trials were conducted over multiple years for two perennial Eriogonum species, E. umbellatum and E. heracleoides. Averaged over 11 years, seed yield of E. umbellatum was maximized by 209 mm/year of spring precipitation plus irrigation. Averaged over 6 years, seed yield of E. heracleoides was maximized by 126 mm/year of applied water. Both species required relatively small amounts of irrigation to help assure seed yield, and the irrigation needed for E. umbellatum could be adjusted by taking spring precipitation into account.